This invention relates to a circuit arrangement comprising an output current path, having one end coupled to a reference potential, for supplying an alternating signal current.
The publication DE 35 90 480 T1 which corresponds to U.S. Pat. No. 4,764,736 Aug. 16,1988, describes an amplifier for a high-frequency signal which is constructed as an integrated circuit comprising at least two stages of d.c. coupled grounded-emitter amplifiers. An emitter resistor is arranged between an emitter of the grounded-emitter amplifier in a second or subsequent stage and ground. A connection external to the integrated circuit is connected to the emitter of the commonemitter amplifier in the second or subsequent stage via a connecting lead. A filter circuit arranged between said connection and the external ground comprises an inductance of the connecting lead and has a low impedance for a given frequency. This is in order to provide a high-frequency amplifier capable of stable operation without any transient phenomena being produced. However, owing to the presence of the filter circuit this known amplifier is only suitable for use with very narrow bandwidths.
U.S. Pat. No. 3,810,256 describes a wide-band transistor amplifier comprising a feedback circuit for maximal negative feedback and a switching circuit, by means of which as a kind of negative feedback only the noise components occurring in the output signal of the amplifier are fed back in order to provide an additional reduction. To this end the transistor amplifier comprises a cascade arrangement of two impedances whose node is connected to the input of a phase inverter, which feeds the phase-inverted noise components into the output circuit of the amplifier. In this circuit arrangement the emitter connection of an amplifier stage also includes a damped parallel resonant circuit for influencing the high-frequency gain. However, this neither provides wide-band operation.
EP-A-264,631 describes a frequency-compensated feedback transistor amplifier having a comparatively large bandwidth and comparatively wide phase and gain limits independently of the intrinsic transconductance of the transistors in the amplifier. The known arrangement comprises a transconductance amplifier and an amplifier stage. The transconductance amplifier supplies an input signal to the amplifier stage and the amplifier stage produces an amplified replica of this input signal. A feedback capacitor is arranged between the output and the input of the amplifier stage and reduces the loop gain by 6 dB per octave with increasing frequency. The capacitor forms a signal path for residual components of the input signal in a manner such that these residual components appear on the amplifier output substantially in phase with the IF output signal.
In circuit arrangements of the type defined in the opening paragraph it appears that for alternating signal currents of comparatively high frequency the amplitude of the alternating signals currents to be produced is distinctly affected by parasitic impedances. Particularly if such a circuit arrangement comprises a current path having one end coupled to a reference potential, for example, ground, even a short connecting lead between the output current path and the reference potential will form a parasitic inductance across which a substantial voltage appears at higher frequencies, which voltage provides a negative feedback by means of which the amplitude of the alternating signal current can be reduced appreciably.